1. Field of the Invention
The present invention relates to a scroll compressor, and particularly, to a scroll compressor capable of increasing a discharge capacity without a size change.
2. Description of the Conventional Art
In general, a compressor converts mechanical energy into compression energy of a compressible fluid, and may be classified into a reciprocating type, a scroll type, a centrifugal type and a vane type.
Unlike the reciprocating compressor using a linear movement of a piston, the scroll compressor sucks, compresses and discharges a gas by using a rotor as the centrifugal type or the vane type compressor.
Such a scroll compressor is commonly used for an air conditioner. To improve cooling and heating efficiency of the air conditioner, a scroll compressor which can vary its capacity has been recently required.
FIG. 1 is a longitudinal sectional view showing a conventional scroll compressor.
As shown, the conventional scroll compressor includes: a casing 1 provided with a gas suction pipe (SP) and a gas discharge pipe (DP); a main frame 2 and a sub frame (not shown) fixedly installed at upper and lower sides of the casing 1, respectively; a driving motor 3 mounted between the main frame 2 and the sub frame, for generating a rotary force; a rotary shaft 4 fixed at the center of the driving motor 3 and penetrating the center of the main frame 2 to transfer a rotary force of the driving motor 3; a fixed scroll 5 fixedly installed on an upper surface of the main frame 2; an orbiting scroll 6 put on an upper surface of the main frame 2 and orbiting in a state of being interlocked with the fixed scroll 5 to thereby form a compression chamber (P); a self-rotation preventing member 7 (Oldham's ring) installed between the orbiting scroll 6 and the main frame 2, for preventing self-rotation of the orbiting scroll 6; and a discharge cover 8 coupled to an upper surface of the fixed scroll, for dividing the inside of the casing 1 into a low pressure portion (S1) and a high pressure portion (S2).
Generally, the fixed scroll 5 fixed at an upper portion of the main frame 2 and the orbiting scroll 6 rotatably installed between the fixed scroll 5 and the main frame 2 are referred to as a compression unit.
A boss receiving portion 2b for an orbiting movement of a boss portion 6b of the orbiting scroll 6 is formed at a central portion of the main frame 2, and a shaft hole 2a for supporting the rotary shaft 4 is formed at the center of the boss receiving portion 2b. 
A wrap 5a forming a compression chamber (P) by being interlocked with a wrap 6a of the orbiting scroll 6 to be explained later is formed at a lower surface of the fixed scroll 5 as an involute shape, and a suction hole 5b is formed at an outermost edge of the wrap 5a. A discharge hole 5c communicating with the high pressure portion (S2) of the casing 1 is formed near the central portion of the fixed scroll 5.
A wrap 6a is formed at an upper surface of the orbiting scroll 6 as an involute shape and is interlocked with the wrap 5a of the fixed scroll 5. A boss portion 6b coupled to an eccentric portion 4a of the rotary shaft 4 and orbiting within the boss receiving portion 2b of the main frame 2 is formed at a central portion of a lower surface of the orbiting scroll.
The conventional scroll compressor having such a structure is operated in the following manner.
When the rotary shaft 4 of the driving motor 3 rotates by applied power, the orbiting scroll 6 does not rotate but orbits by the self-rotation preventing member 7.
At this time, a compression chamber (P) is formed between the wrap 6a of the orbiting scroll 6 and the wrap 5a of the fixed scroll 5. By a constant orbiting movement of the orbiting scroll 6, the compression chamber (P) moves a refrigerant gas, which has been introduced from the suction hole 5b, toward the discharge hole 5c, and then discharges the gas.
In other words, the refrigerant gas is sucked into the low pressure portion (S1) of the casing 1 through the gas suction pipe (SP), is introduced toward an outermost edge of the compression chamber (P) through the suction hole 5b of the fixed scroll 5, and then is compressed, gradually moving toward the inside of the compression chamber (P) by a continuous orbiting movement of the orbiting scroll 6. The compressor refrigerant gas is discharged to the high pressure portion (S2) of the casing 1 through the discharge hole 5c of the fixed scroll 5.
However, the conventional scroll compressor having such a structure has a limit in increasing its capacity because the refrigerant gas is compressed only in the compression chamber (P) formed by the orbiting scroll 6 and the fixed scroll 5.